Chicken with a slow molt; had injury. How to help her.

I have a 2 year old chicken that had a leg band grow into her leg. I removed it, but her leg is fatter on one side and it took about 1 month for that injury to heal. It's now been 3-4 months and she looks like she is in a perpectual state of molt. I checked for mites, didn't seen any evidence. She eats, drinks and acts healthy otherwise. She shivers though, because it's cold and she doesn't have a nice fluffy layer of feathers. Something is obviously lacking. What does she need and how can I help her. Vitamins?